U.S. patent number 9,551,693 [Application Number 14/383,275] was granted by the patent office on 2017-01-24 for photoacoustic wave measurement device, method, program, and recording medium.
This patent grant is currently assigned to ADVANTEST CORPORATION. The grantee listed for this patent is ADVANTEST CORPORATION. Invention is credited to Taiichiro Ida, Yasushi Kawaguchi.
United States Patent |
9,551,693 |
Ida , et al. |
January 24, 2017 |
Photoacoustic wave measurement device, method, program, and
recording medium
Abstract
A photoacoustic wave measurement device includes: (a) a
pulsed-light outputter that outputs a pulsed light; (b) an
arrangement member disposed between a pulsed-light output end of
the pulsed-light outputter and a measurement object, the
arrangement member being adapted to allow the pulsed light to pass
therethrough; and (c) a photoacoustic wave detector that receives a
photoacoustic wave generated by the measurement object by the
pulsed light and that converts the photoacoustic wave into an
electric signal, the photoacoustic wave measurement device being
adapted to receive the electric signal from a photoacoustic wave
sensor in which the photoacoustic wave detector is farther from the
measurement object than the pulsed-light output end. The
photoacoustic wave measurement device further includes: an electric
signal recording section that receives and records the electric
signal from the photoacoustic wave sensor; a noise timing
estimation section that estimates timing of occurrence of noise in
the electric signal, from a thickness of the arrangement member;
and a noise removal section that removes the electric signal at the
timing estimated, from contents recorded by the electric signal
recording section.
Inventors: |
Ida; Taiichiro (Gunma,
JP), Kawaguchi; Yasushi (Saitama, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
ADVANTEST CORPORATION |
Tokyo |
N/A |
JP |
|
|
Assignee: |
ADVANTEST CORPORATION (Tokyo,
JP)
|
Family
ID: |
49711799 |
Appl.
No.: |
14/383,275 |
Filed: |
May 2, 2013 |
PCT
Filed: |
May 02, 2013 |
PCT No.: |
PCT/JP2013/063229 |
371(c)(1),(2),(4) Date: |
September 05, 2014 |
PCT
Pub. No.: |
WO2013/183399 |
PCT
Pub. Date: |
December 12, 2013 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20150047433 A1 |
Feb 19, 2015 |
|
Foreign Application Priority Data
|
|
|
|
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Jun 4, 2012 [JP] |
|
|
2012-127103 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B
8/429 (20130101); G01N 29/2418 (20130101); G01N
29/38 (20130101); G01N 29/44 (20130101); G01N
29/343 (20130101); A61B 5/0095 (20130101); G01N
21/1702 (20130101); A61B 8/5269 (20130101); G01N
2021/1708 (20130101); A61B 8/4281 (20130101) |
Current International
Class: |
G01N
29/34 (20060101); G01N 21/17 (20060101); G01N
29/24 (20060101); G01N 29/44 (20060101); A61B
5/00 (20060101); G01N 29/38 (20060101); A61B
8/00 (20060101); A61B 8/08 (20060101) |
Field of
Search: |
;73/645 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2011-055902 |
|
Mar 2011 |
|
JP |
|
2011-183149 |
|
Sep 2011 |
|
JP |
|
2011-229660 |
|
Nov 2011 |
|
JP |
|
2012-24460 |
|
Feb 2012 |
|
JP |
|
2012-29715 |
|
Feb 2012 |
|
JP |
|
2012-86037 |
|
May 2012 |
|
JP |
|
Other References
Search Report issued by E.P.O. patent office in E.P.O. Patent
Application No. 13800997.2, dated Mar. 3, 2016. cited by applicant
.
U.S. Appl. No. 14/397,939 to Taiichiro Ida, filed Oct. 30, 2014.
cited by applicant .
U.S. Appl. No. 14/382,596 to Taiichiro Ida, filed Sep. 3, 2014.
cited by applicant .
U.S. Appl. No. 14/383,292 to Yasushi Kawaguchi et al., filed Sep.
5, 2014. cited by applicant .
Search report from International Bureau of WIPO, Application No.
PCT/JP2013/063229, mail date is Jun. 4, 2013. cited by
applicant.
|
Primary Examiner: Saint Surin; J M
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
The invention claimed is:
1. A photoacoustic wave measurement device comprising: a
pulsed-light outputter that outputs a pulsed light; an arrangement
spacer disposed between a pulsed-light output end of the
pulsed-light outputter and a measurement object, the arrangement
spacer being adapted to allow the pulsed light to pass
therethrough; a photoacoustic wave detector that receives a
photoacoustic wave generated by the measurement object by the
pulsed light and that converts the photoacoustic wave into an
electric signal, the photoacoustic wave measurement device being
configured to receive the electric signal from a photoacoustic wave
sensor in which the photoacoustic wave detector is farther from the
measurement object than the pulsed-light output end; an electric
signal recorder that receives and records the electric signal from
the photoacoustic wave sensor; a noise timing estimator that
estimates timing of occurrence of noise in the electric signal,
from a thickness of the arrangement spacer; and a noise remover
that removes the electric signal at the timing estimated, from
contents recorded by the electric signal recorder.
2. The photoacoustic wave measurement device according to claim 1,
wherein the arrangement spacer has such a sufficient thickness that
noise to be detected by the photoacoustic wave detector after a
start time of detection of the photoacoustic wave starts to be
detected after an end time of the detection of the photoacoustic
wave.
3. The photoacoustic wave measurement device according to claim 1,
wherein the pulsed-light outputter is an optical fiber.
4. The photoacoustic wave measurement device according to claim 1,
wherein the photoacoustic wave detector is a piezoelectric
element.
5. A method of measuring a photoacoustic wave by using a
photoacoustic wave measurement device including: (a) a pulsed-light
outputter that outputs a pulsed light; (b) an arrangement spacer
disposed between a pulsed-light output end of the pulsed-light
outputter and a measurement object, the arrangement spacer being
adapted to allow the pulsed light to pass therethrough; and (c) a
photoacoustic wave detector that receives a photoacoustic wave
generated by the measurement object by the pulsed light and that
converts the photoacoustic wave into an electric signal, the
photoacoustic wave measurement device being configured to receive
the electric signal from a photoacoustic wave sensor in which the
photoacoustic wave detector is farther from the measurement object
than the pulsed-light output end, said method comprising: receiving
and recording the electric signal from the photoacoustic wave
sensor; estimating timing of occurrence of noise in the electric
signal, from a thickness of the arrangement spacer; and removing
the electric signal at the timing estimated, from contents recorded
by the receiving and recording of the electric signal.
6. A program of instructions stored on a non-transitory
computer-readable medium for execution by a computer to perform a
process of measuring a photoacoustic wave by using a photoacoustic
wave measurement device including: (a) a pulsed-light outputter
that outputs a pulsed light; (b) an arrangement spacer disposed
between a pulsed-light output end of the pulsed-light outputter and
a measurement object, the arrangement spacer being adapted to allow
the pulsed light to pass therethrough; and (c) a photoacoustic wave
detector that receives a photoacoustic wave generated by the
measurement object by the pulsed light and that converts the
photoacoustic wave into an electric signal, the photoacoustic wave
measurement device being configured to receive the electric signal
from a photoacoustic wave sensor in which the photoacoustic wave
detector is farther from the measurement object than the
pulsed-light output end, said process comprising: receiving and
recording the electric signal from the photoacoustic wave sensor;
estimating timing of occurrence of noise in the electric signal,
from a thickness of the arrangement spacer; and removing the
electric signal at the timing estimated, from contents recorded by
the receiving and recording of the electric signal.
7. A non-transitory computer-readable medium having a program of
instructions for execution by a computer to perform a process of
measuring a photoacoustic wave by using a photoacoustic wave
measurement device including: (a) a pulsed-light outputter that
outputs a pulsed light; (b) an arrangement spacer disposed between
a pulsed-light output end of the pulsed-light outputter and a
measurement object, the arrangement spacer being adapted to allow
the pulsed light to pass therethrough; and (c) a photoacoustic wave
detector that receives a photoacoustic wave generated by the
measurement object by the pulsed light and that converts the
photoacoustic wave into an electric signal, the photoacoustic wave
measurement device being configured to receive the electric signal
from a photoacoustic wave sensor in which the photoacoustic wave
detector is farther from the measurement object than the
pulsed-light output end, said process comprising: receiving and
recording the electric signal from the photoacoustic wave sensor;
estimating timing of occurrence of noise in the electric signal,
from a thickness of the arrangement spacer; and removing the
electric signal at the timing estimated, from contents recorded by
the receiving and recording of the electric signal.
Description
FIELD OF THE INVENTION
The present invention relates to photoacoustic sensors.
BACKGROUND ART
Photoacoustic sensors are conventionally known to measure a
photoacoustic signal generated by irradiating an object to be
measured (e.g. biological object) with pulsed light (see, for
example, Patent Document 1 (Japanese Unexamined Patent Publication
No. 2011-229660)).
SUMMARY OF THE INVENTION
Such a photoacoustic signal obtained by the photoacoustic sensor,
however, might have noise superimposed thereon.
Accordingly, it is an object of the present invention to reduce
noise to be superimposed on the photoacoustic signal obtained by
the photoacoustic wave measurement device.
According to the present invention, a photoacoustic wave
measurement device includes: (a) a pulsed-light outputter that
outputs a pulsed light; (b) an arrangement member disposed between
a pulsed-light output end of the pulsed-light outputter and a
measurement object, the arrangement member being adapted to allow
the pulsed light to pass therethrough; and (c) a photoacoustic wave
detector that receives a photoacoustic wave generated by the
measurement object by the pulsed light and that converts the
photoacoustic wave into an electric signal, the photoacoustic wave
measurement device being adapted to receive the electric signal
from a photoacoustic wave sensor in which the photoacoustic wave
detector is farther from the measurement object than the
pulsed-light output end, wherein the photoacoustic wave measurement
device further includes: an electric signal recording section that
receives and records the electric signal from the photoacoustic
wave sensor; a noise timing estimation section that estimates
timing of occurrence of noise in the electric signal, from a
thickness of the arrangement member; and a noise removal section
that removes the electric signal at the timing estimated, from
contents recorded by the electric signal recording section.
According to the thus constructed photoacoustic wave measurement
device, a photoacoustic wave measurement device including: (a) a
pulsed-light outputter that outputs a pulsed light; (b) an
arrangement member disposed between a pulsed-light output end of
the pulsed-light outputter and a measurement object, the
arrangement member being adapted to allow the pulsed light to pass
therethrough; and (c) a photoacoustic wave detector that receives a
photoacoustic wave generated by the measurement object by the
pulsed light and that converts the photoacoustic wave into an
electric signal, the photoacoustic wave measurement device being
adapted to receive the electric signal from a photoacoustic wave
sensor in which the photoacoustic wave detector is farther from the
measurement object than the pulsed-light output end, can be
provided. An electric signal recording section receives and records
the electric signal from the photoacoustic wave sensor. A noise
timing estimation section estimates timing of occurrence of noise
in the electric signal, from a thickness of the arrangement member.
A noise removal section removes the electric signal at the timing
estimated, from contents recorded by the electric signal recording
section.
According to the photoacoustic wave measurement device of the
present invention, the arrangement member may have such a
sufficient thickness that noise to be detected by the photoacoustic
wave detector after a start time of detection of the photoacoustic
wave starts to be detected after an end time of the detection of
the photoacoustic wave.
According to the photoacoustic wave measurement device of the
present invention, the pulsed-light outputter may be an optical
fiber.
According to the photoacoustic wave measurement device of the
present invention, the photoacoustic wave detector may be a
piezoelectric element.
The present invention is a method of measuring a photoacoustic wave
by using a photoacoustic wave measurement device including: (a) a
pulsed-light outputter that outputs a pulsed light; (b) an
arrangement member disposed between a pulsed-light output end of
the pulsed-light outputter and a measurement object, the
arrangement member being adapted to allow the pulsed light to pass
therethrough; and (c) a photoacoustic wave detector that receives a
photoacoustic wave generated by the measurement object by the
pulsed light and that converts the photoacoustic wave into an
electric signal, the photoacoustic wave measurement device being
adapted to receive the electric signal from a photoacoustic wave
sensor in which the photoacoustic wave detector is farther from the
measurement object than the pulsed-light output end, the method
including: an electric signal recording step that receives and
records the electric signal from the photoacoustic wave sensor; a
noise timing estimation step that estimates timing of occurrence of
noise in the electric signal, from a thickness of the arrangement
member; and a noise removal step that removes the electric signal
at the timing estimated, from contents recorded by the electric
signal recording step.
The present invention is a program of instructions for execution by
a computer to perform a process of measuring a photoacoustic wave
by using a photoacoustic wave measurement device including: (a) a
pulsed-light outputter that outputs a pulsed light; (b) an
arrangement member disposed between a pulsed-light output end of
the pulsed-light outputter and a measurement object, the
arrangement member being adapted to allow the pulsed light to pass
therethrough; and (c) a photoacoustic wave detector that receives a
photoacoustic wave generated by the measurement object by the
pulsed light and that converts the photoacoustic wave into an
electric signal, the photoacoustic wave measurement device being
adapted to receive the electric signal from a photoacoustic wave
sensor in which the photoacoustic wave detector is farther from the
measurement object than the pulsed-light output end, the process
including: an electric signal recording step that receives and
records the electric signal from the photoacoustic wave sensor; a
noise timing estimation step that estimates timing of occurrence of
noise in the electric signal, from a thickness of the arrangement
member; and a noise removal step that removes the electric signal
at the timing estimated, from contents recorded by the electric
signal recording step.
The present invention is a computer-readable medium having a
program of instructions for execution by a computer to perform a
process of measuring a photoacoustic wave by using a photoacoustic
wave measurement device including: (a) a pulsed-light outputter
that outputs a pulsed light; (b) an arrangement member disposed
between a pulsed-light output end of the pulsed-light outputter and
a measurement object, the arrangement member being adapted to allow
the pulsed light to pass therethrough; and (c) a photoacoustic wave
detector that receives a photoacoustic wave generated by the
measurement object by the pulsed light and that converts the
photoacoustic wave into an electric signal, the photoacoustic wave
measurement device being adapted to receive the electric signal
from a photoacoustic wave sensor in which the photoacoustic wave
detector is farther from the measurement object than the
pulsed-light output end, the process including: an electric signal
recording step that receives and records the electric signal from
the photoacoustic wave sensor; a noise timing estimation step that
estimates timing of occurrence of noise in the electric signal,
from a thickness of the arrangement member; and a noise removal
step that removes the electric signal at the timing estimated, from
contents recorded by the electric signal recording step.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a functional block diagram showing the configuration of a
photoacoustic wave measurement device 40 according to one
embodiment of the present invention;
FIG. 2 is a cross-sectional view of the photoacoustic wave sensor 1
according to the one embodiment of the present invention;
FIG. 3(a) shows a cross-sectional view of another photoacoustic
wave sensor 1 in a modified example (a), and FIG. 3(b) shows a
cross-sectional view of a further photoacoustic wave sensor 1 in
another modified example (b); and
FIG. 4 shows a graph of waveforms detected by the photoacoustic
wave sensors 1 in the modified examples (a) and (b) (see FIGS. 3(a)
and (b)), and by the photoacoustic wave sensor 1 in the one
preferred embodiment of the present invention (see FIG. 2).
MODES FOR CARRYING OUT THE INVENTION
A description will now be given of an embodiment of the present
invention referring to drawings.
FIG. 1 is a functional block diagram showing the configuration of a
photoacoustic wave measurement device 40 according to one
embodiment of the present invention. The photoacoustic wave
measurement device 40 receives an electric signal from a
photoacoustic wave sensor 1. The photoacoustic wave measurement
device 40 includes a waveform detector 42, a spacer thickness
recording section 43, a noise timing estimation section 44, a
waveform recording section (i.e. electric signal recording section)
46, and a noise removal section 48.
FIG. 2 is a cross-sectional view of the photoacoustic wave sensor 1
according to the one embodiment of the present invention. The
photoacoustic wave sensor 1 includes a case 10, a backing member
12, a piezoelectric element (i.e. photoacoustic wave detector) 14,
an electrode 16, a spacer 18, an optical fiber (i.e. pulsed-light
outputter) 20, and external spacers (i.e. arrangement members) 32,
34, and 36.
The photoacoustic wave sensor 1 shown in FIG. 2 is more preferable
than the photoacoustic wave sensor 1 shown in FIG. 3. This is
because noise B (see FIG. 4) is not superimposed on a photoacoustic
wave W (see FIG. 4) as described later.
The case 10 is a case for accommodating therein the backing member
12, the piezoelectric element 14, the electrode 16, and the spacer
18. The spacer 18 is in contact with the bottom surface of the case
10, and the electrode 16 is mounted on the spacer 18. The
piezoelectric element 14 is mounted on the electrode 16, and the
backing member 12 is mounted on the piezoelectric element 14.
The backing member 12 serves as a backing material made of epoxy
resin. The piezoelectric element (i.e. photoacoustic wave detector)
14 receives a pressure caused by compression waves or the like and
converts the pressure into a voltage. The electrode 16 receives the
voltage from the piezoelectric element 14 and supplies the voltage
to the photoacoustic wave measurement device 40. The electrode 16
is, for example, a gold electrode. The spacer 18 allows the
compression waves to pass therethrough. The spacer 18 is a
transparent spacer, for example, made of polystyrene.
The optical fiber (i.e. pulsed light outputter) 20 outputs a pulsed
light P from a pulsed-light output end 20a. The optical fiber 20 is
connected to a pulse light source (not shown) outside the
photoacoustic wave sensor 1. The optical fiber 20 penetrates
through the case 10, the backing member 12, the piezoelectric
element 14, the electrode 16, and the spacer 18.
The external spacers (i.e. arrangement members) 32, 34, and 36 are
disposed between the pulsed-light output end 20a and a measurement
object 2 so as to allow the pulsed light P to pass therethrough.
The external spacer 32 is in contact with the case 10 and the
pulsed-light output end 20a. The external spacer 36 is in contact
with the measurement object 2. The external spacer 34 is disposed
between the external spacer 32 and the external spacer 36.
The external spacer (i.e. arrangement member) 32 is a spacer, for
example, made of white polycarbonate of 1.5 mm in thickness. Each
of the external spacers (i.e. arrangement members) 34 and 36 is a
transparent spacer made of polystyrene of 4.0 mm in thickness. Note
that the external spacers 32, 34, and 36 may be integrally formed
together.
The measurement object 2 is, for example, a finger cushion of a
human being. The measurement object 2 includes a blood vessel 2a.
When receiving the pulsed light P, the blood vessel 2a generates a
photoacoustic wave W. The piezoelectric element 14 receives the
photoacoustic wave W and converts the wave W into an electric
signal (for example, in the form of a voltage). The piezoelectric
element 14 is farther from the measurement object 2 than the
pulsed-light output end 20a.
FIG. 3(a) shows a cross-sectional view of another photoacoustic
wave sensor 1 in a modified example (a), and FIG. 3(b) shows a
cross-sectional view of a further photoacoustic wave sensor 1 in
another modified example (b).
The modified example (a) is one obtained by removing the external
spacers 32 and 36 from the photoacoustic wave sensor 1 shown in
FIG. 2. The modified example (b) is one obtained by removing the
external spacer 36 from the photoacoustic wave sensor 1 shown in
FIG. 2.
Returning to FIG. 1, the configuration of the photoacoustic wave
measurement device 40 will be described below.
The waveform detector 42 receives an electric signal (for example,
in the form of a voltage) from the electrode 16 and detects its
waveform, and sends the detected waveform to the waveform recording
section 46.
The spacer thickness recording section 43 records the thickness of
the external spacer.
The noise timing estimation section 44 estimates timing of
occurrence of noise in the electric signal (for example, in the
form of the voltage), from the thickness of the external spacer
(i.e. arrangement member) recorded by the spacer thickness
recording portion 43.
The waveform recording section (i.e. electric signal recording
section) 46 receives an electric signal from the photoacoustic wave
sensor 1 via the waveform detector 42, and records the electric
signal therein (see FIG. 4).
The noise removal section 48 removes the electric signal at the
timing estimated, from the contents recorded by the waveform
recording section (i.e. electric signal recording section) 46.
Next, the operation of the embodiment in the present invention will
be described below.
First, an external pulsed light source (not shown) emits a pulsed
light P, and the pulsed light P passes through the optical fiber
20. Then, the pulsed light P is output from the pulsed-light output
end 20a. The pulsed light P is applied to the measurement object 2
through the external spacers 32, 34, and 36.
The pulsed light P reaches the blood vessel 2a of the measurement
object 2. At this time, the blood vessel 2a absorbs the pulsed
light P and is warmed and is then adiabatically expanded. Thus, the
compression waves (i.e. photoacoustic waves W) are output from the
blood vessel 2a.
The photoacoustic waves W reach the piezoelectric element 14
through the measurement object 2, the external spacers 36, 34, and
32, the spacer 18, and the electrode 16. The piezoelectric element
14 converts the pressure produced by the photoacoustic wave W into
an electric signal (for example, in the form of a voltage). The
voltage is taken out to the outside via the electrode 16, and then
fed to the waveform detector 42 of the photoacoustic wave
measurement device 40.
FIG. 4 shows a graph of waveforms detected by the photoacoustic
wave sensors 1 in the modified examples (a) and (b) (see FIGS. 3(a)
and (b)), and by the photoacoustic wave sensor 1 in the one
preferred embodiment of the present invention (see FIG. 2). Such
detected waveforms are obtained by the waveform detector 42 and fed
to the waveform recording section 46.
Each of the detected waveforms in the modified examples (a) and (b)
and the one preferred embodiment of the present invention includes
noise A, photoacoustic wave W, and noise B.
The photoacoustic wave W is a photoacoustic wave generated from the
blood vessel 2a of the measurement object 2. The photoacoustic wave
has a waveform which is to be detected. During a period of time
indicated by a bidirectional arrow, the photoacoustic wave W is
detected.
The noise A is noise detected by the piezoelectric element 14
before a time t1 when the photoacoustic wave W starts to be
detected. In the embodiment of the present invention as well as the
modified examples (a) and (b), the noise A is not superimposed on
the photoacoustic wave W.
The noise B is noise detected by the piezoelectric element 14 after
the time t1 when the photoacoustic wave W starts to be detected. In
the modified examples (a) and (b), the noise B is superimposed on
the photoacoustic wave W due to insufficient thickness of the
external spacer.
In the preferred embodiment of the present invention, however, the
noise B is not superimposed on the photoacoustic wave W. That is,
in the preferred embodiment of the present invention, a time t3
when the noise B starts to be detected comes after a time t2 of the
end of detecting the photoacoustic wave W because of a sufficient
thickness of the external spacers 32, 34, and 36.
The thicknesses of the external spacers in respective cases are as
follows: (the thickness of the external spacer in the modified
example (a))<(the thickness of the external spacer in the
modified example (b))<(the thickness of the external spacer in
the preferred embodiment of the present invention). As the
thickness of the external spacer is increased, the time required
for the photoacoustic wave W to reach the piezoelectric element 14
becomes longer. As a result, the detection start time of the
photoacoustic wave W in the modified example (b) is delayed more
than that in the modified example (a), whereas the detection start
time of the photoacoustic wave W in the preferred embodiment of the
present invention is delayed more than that in the modified example
(b).
Further, the time when the noise B starts to be detected is also
delayed more as the thickness of the external spacer is increased.
However, it has been newly found from the detected waveforms shown
in FIG. 4 that the delay of the detection start time of the noise B
due to the increase in thickness of the external spacer is much
larger than the delay of the detection start time of the
photoacoustic wave W.
This is supposed to be because the photoacoustic wave generated in
the vicinity of the pulsed-light output end 20a is reflected by a
boundary surface between the external spacer 36 and the measurement
object 2, and then reaches the piezoelectric element 14 to cause
the noise B. In this case, the detection start time of the noise B
is delayed only by a time that requires the photoacoustic wave W to
travel about twice as long as the thickness of the external spacer.
Thus, the detection start time t3 of the noise B is delayed only by
about a time determined by the formula of (external spacer
thickness)/(speed of photoacoustic wave W) with respect to the
detection start time t1 of the photoacoustic wave W.
By use of the above-mentioned principle, the noise timing
estimation section 44 estimates timing of occurrence of the noise B
in the electric signal. Specifically, the noise timing estimation
section 44 reads a thickness of the external spacers from the
spacer thickness recording section 43, determines a value of t3-t1
by dividing the thickness of the external spacers by the speed of
the photoacoustic wave W, and then sends data on the value t3-t1
determined to the noise removal section 48.
Additionally, since the photoacoustic wave W is larger in size than
the noise B, the time when the waveform of the photoacoustic wave W
exceeds a predetermined threshold is regarded as the detection
start time t1 of the photoacoustic wave W. In this way, the time t1
can be determined. The noise removal section 48 determines the time
t3 by adding the value of t3-t1 fed from the noise timing
estimation section 44 to the time t1 thus-obtained, and then
deletes a waveform produced after the time t3 from the contents
recorded in the waveform recording section (i.e. electric signal
recording section) 46.
When the photoacoustic wave W and the noise B are not superimposed
on each other, like the preferred embodiment of the present
invention, only the noise B can be deleted, which is preferable.
However, even though the photoacoustic wave W and the noise B are
superimposed on each other as shown in the modified examples (a)
and (b), the waveform produced after the time t3 may be removed
from the contents recorded in the waveform recording section 46 by
the noise removal section 48 if the photoacoustic wave W is allowed
to be slightly lost. Although in this case, the photoacoustic wave
W is slightly removed, the noise B can also be removed.
In the photoacoustic wave measurement device 40 in the embodiment
of the present invention, the time (t3-t1) can be determined in the
form of (external spacer thickness)/(speed of photoacoustic wave W)
by the noise timing estimation section 44. In this way, the
embodiment of the present invention can delete the waveform
produced after the time t3, which is a time after the elapse of the
period of time (t3-t1) following the detection start time t1 of the
photoacoustic wave W, from the contents recorded in the waveform
recording section (i.e. electric signal recording section) 46 to
thereby remove the noise B.
The embodiments described above can be implemented in the following
way. A computer with a CPU, a hard disk, and a media (floppy
(trademark) disk, CD-ROM, etc.) reader is adapted to read media
that store therein programs for achieving the above-mentioned
components, for example, the waveform detector 42, the spacer
thickness recording section 43, the noise timing estimation section
44, the waveform recording section 46, and the noise removal
section 48. Then, the media read are installed in the hard disk.
Even this method can achieve the above-mentioned functions.
* * * * *